The Cotter Dam open day scheduled for Sunday has been postponed with persistent rainfall over the past few days.
The managing director of ACTEW Water, Mark Sullivan, attributed safety concerns to the move.
"ACTEW Water and our construction partners have had to take the precautionary action of postponing this weekend's Cotter Dam open day in order to ensure that safety is maintained for our visitors," Mr Sullivan said.
"We apologise for any inconvenience this may cause and we hope people can make it to the rescheduled day on Sunday 23 June from 8.30am to 3.30pm."
Data from the Bureau of Meteorology shows that water storage in the ACT is 85.2 per cent. The Cotter Dam extension will increase capacity by 35 per cent.
"It would be fantastic to get at least average rainfall over the coming seasons, as it will mean that Canberra's new dam, which is already storing water for the future, will fill even faster," Mr Sullivan said.